Hypsodonty in Pleistocene ground sloths
M. SUSANA BARGO, GERARDO DE IULIIS, and SERGIO F. VIZCAÍNO
Bargo, M.S., De Iuliis, G., and Vizcaíno, S.F. 2006. Hypsodonty in Pleistocene ground sloths. Acta Palaeontologica
Polonica 51 (1): 53–61.
Although living sloths (Xenarthra, Tardigrada) are represented by only two genera, their fossil relatives form a large and
diverse group. The evolution of hypsodonty, the crown height of a tooth, has traditionally been viewed as a response to di−
etary shifts toward abrasive vegetation. But recent work indicates that hypsodonty is also due to the higher prevalence of
grit and dust in more open environments. The teeth of sloths are both high−crowned and open−rooted, or hypselodont, but
distinctions between the selective factors acting to produce differing degrees of hypsodonty have not been rigorously con−
sidered. A comparative analysis of hypsodonty was performed in eleven species of Pleistocene sloths. It suggests that dif−
ferences in hypsodonty may be explained by dietary preferences, habitat and habits. Among mylodontids, morphologic
and biomechanical analyses indicate that hypsodonty was unlikely to be due solely to feeding behavior, such as grazing.
Some mylodontids (e.g., Scelidotherium leptocephalum, Lestodon armatus, Glossotherium robustum, Mylodon darwini)
were capable diggers that likely dug for food, and ingestion of abrasive soil particles probably played a considerable role
in shaping their dental characteristics. Increased hypsodonty over time in Paramylodon harlani, however, is apparently
due to a change in habitat from closed to more open environments. Geographical distributions of the megatheriids
Eremotherium and Megatherium indicate differing habitats as possible factors in hypsodonty differences. In summary,
among Tardigrada hypsodonty is apparently affected by diet, habitat and habit. The absence of enamel must be responsi−
ble for much of the hypsodonty observed in xenarthrans, which obscures the interpretation of contribution of each of the
mentioned factors.
Key wo r d s: Pleistocene, Xenarthra, Tardigrada, hypsodonty, diet, habits, habitat.
M. Susana Bargo [[email protected]] and Sergio F. Vizcaíno [[email protected]], Departamento
Científico Paleontología de Vertebrados, Museo de La Plata, CIC−CONICET, Paseo del Bosque s/n, B1900FWA La
Plata, Argentina;
Gerardo De Iuliis [[email protected]], Department of Zoology, University of Toronto, 25 Harbord Street, Toronto,
Ontario, Canada M5S 3G5 and Faculty of Community Services and Health Sciences, George Brown College, Toronto,
Ontario, Canada M5A 1J5.
Introduction
Hypsodonty has traditionally been linked to dietary prefer−
ences, particularly to grazing habits (Simpson 1951, 1953;
McNaughton et al. 1985; MacFadden 1997). These authors
considered the increase in tooth crown height as an adaptation
for an abrasive herbivorous diet, consisting primarily of gras−
ses. Fortelius (1985), Janis (1988; 1995), and Janis and For−
telius (1988), in their analyses of extinct and extant ungulates,
noted that another important factor in determining hypso−
donty is the accumulated grit or dust on plants consumed in
more open habitats. Ungulates feeding at ground level in open
habitats, even with diets containing little grass, are more
hypsodont than those living and foraging in closed habitats.
In other words, both habitat preference (and therefore abra−
sive particles such as dust and grit) and dietary preference are
highly important determinants of degree of hypsodonty. Wil−
liams and Kay (2001) examined the evolution of increased
molar crown height in extant African ungulates and South
American rodents in relation to ecological and behavioral
variables. They found that both diet and exogenous dust and
grit play a role in shaping the evolution of hypsodonty.
Acta Palaeontol. Pol. 51 (1): 53–61, 2006
Xenarthra comprises armadillos and glyptodonts (Cingu−
lata), anteaters (Vermilingua), and sloths (Tardigrada), and
are considered by some authors as one of the four major
clades of placental mammals (the other three being Afro−
theria, Euarchontoglires and Laurasiatheria; see Murphy et
al. 2001; Madsen et al. 2001; Delsuc et al. 2003). Other au−
thors, following McKenna (1975), consider the Xenarthra as
the sister group to all other placentals, the Epitheria. While
debate continues on the relationships among these groups of
mammals, it does not change the fact that xenarthran dental
morphology is extremely different from that of the other pla−
cental mammals. For convenience, we refer to non−xenar−
thran placental mammals as “epitherians”. The homodont
teeth, which lack enamel, are reduced in number and are
hypsodont and ever growing (i.e., hypselodont). As the ho−
mology of xenarthran teeth with those of other mammals has
not been established, xenarthran teeth have traditionally been
referred to as molariforms. Some sloths also have a canine−
like tooth, termed a caniniform, anteriorly in the oral cavity.
Although hypsodonty is well developed in all Tardigrada,
the giant Pleistocene ground sloths apparently achieved the
greatest development of this feature (Figs. 1, 2). A great
http://app.pan.pl/acta51/app51−053.pdf
number and diversity of small and medium sized tardigrades,
probably arboreal in habits and folivorous in diet have been
recorded from the Santacrucian and Friasian South Ameri−
can ages (early and middle Miocene) (Scillato−Yané 1986;
White 1997). Based on their narrow muzzles and teeth bear−
ing cutting, transverse lophs, McDonald (1997) suggested
that these early forms might have been browsers. Thus, it
might be expected that they were less hypsodont than the
Pleistocene forms, especially if they inhabited more closed
and forested environments. Scillato−Yané et al. (1987) indi−
cated that increased hypsodonty was among the evolutionary
trends of the Nothrotheriinae sensu Hoffstetter 1958 (late
Oligocene to Pleistocene), but this trend has not been quanti−
fied. Nothrotheres are excluded from this analysis. As the
dental formula of Pleistocene nothrotheres is reduced, com−
pared to mylodontids and megatheriids, due to loss of the
most anterior tooth, equivalent comparisons cannot be made
with the taxa studied here. Megalonychids are also excluded
due to inaccessibility of material.
The hypsodonty indices for ungulates calculated by Janis
(1988, 1995) and Janis and Fortelius (1988) are determined
as unworn m3 height divided by m3 width, as the third lower
molar is usually the tooth with the greatest crown height in
ungulates. However, as the cheek teeth of xenarthrans cannot
be homologized with those of “epitherians”, this hypsodonty
index is unsuitable for sloths. A further consideration is that
the hypselodont teeth of xenarthrans have very delicate basal
portions that are almost never preserved. For these reasons,
xenarthran specialists have recognized that the relative in−
crease in depth of the jaw in sloths reflects increased hypso−
donty. Kraglievich (1930) noted that depth of the mandible is
important in determining evolutionary relationships among
megatheriines. Later, Zetti (1964) made the first attempt to
quantify the degree of hypsodonty in megatheres and devel−
oped a Hypsodonty Index where a higher HI reflects in−
creased hypsodonty. De Iuliis (1996), De Iuliis and Cartelle
(1999), and Saint−André and De Iuliis (2001) applied this in−
dex to various megatheriine species. Similarly, McDonald
(1995) compared hypsodonty in North American mylodon−
tine ground sloths using the same index.
The goal of this work is to quantify the degree of hypso−
donty in different species of Pleistocene megatheriid and mylo−
dontid ground sloths in order to determine whether hypsodonty
is correlated with dietary behavior, habits, and habitat. Bargo
and De Iuliis (1999) made a first approach on this theme, ana−
lyzing hypsodonty of the two giant Pleistocene megatheres,
Megatherium americanum Cuvier, 1796, and Eremotherium
laurillardi (Lund, 1842). Saint−André and De Iuliis (2001)
compared hypsodonty among several Megatherium species
(Megatherium altiplanicum Saint−André and De Iuliis, 2001,
M. medinae Philippi, 1893, M. tarijense Gervais and Ameg−
hino, 1880); and De Iuliis and Cartelle (1999) between Eremo−
therium laurillardi and Eremotherium eomigrans De Iuliis and
Cartelle, 1999. Neither study, however, noted possible correla−
tions of hypsodonty with diet, habits or habitat.
ACTA PALAEONTOLOGICA POLONICA 51 (1), 2006
50 mm
54
Fig. 1. A. MLP 2−3, molariform of Megatherium americanum Cuvier,
1796, Pleistocene, Buenos Aires province, Argentina. B. UF 162356,
molariform of Eremotherium eomigrans De Iuliis and Cartelle, 1999, Pleis−
tocene, Alachua, Florida, USA. Because of the homodonty of the upper and
lower megatheriine molariforms, determining the position of the isolated
teeth is not reliable (except for M1, M5, and m5, but these do not have the
ridges and grooves so prominent as in the illustrated material); thus, we
have not attempted to identify the exact position of these teeth, but only fig−
ure them to show their occlusal features and the development of the tooth
crown height.
Institutional abbreviations.—AMNH, American Museum of
Natural History, New York, USA; BM(NH), Natural History
Museum, London, England; F:AM, Frick Collection, Ameri−
can Museum of Natural History, New York, USA; FMNH,
Field Museum of Natural History, Chicago, USA; ILSB,
Instituto de La Salle, Bogotá, Colombia; LACMHC, Los An−
geles County Museum, Hancock Collection, Los Angeles,
USA; MACN, Museo Argentino de Ciencias Naturales, Bue−
nos Aires, Argentina; MCL, Museu de Ciências Naturais
da Pontifícia Universidade Católica de Minas Gerais, Belo
Horizonte, Brazil; MHM, Museo Histórico Municipal, Gen−
eral Belgrano, Provincia de Buenos Aires, Argentina; MLP,
Museo de La Plata, La Plata, Argentina; MMCIPAS, Museo
Municipal y Centro de Investigaciones Paleontológicas de
Salto, Buenos Aires Province, Argentina; MMP, Museo Mu−
nicipal de Ciencias Naturales, Mar del Plata, Argentina;
MNHN, Museo Nacional de Historia Natural de Montevi−
deo, Uruguay; MNHNM, Museo Nacional de Historia Natu−
ral, Madrid, Spain; MNHNP, Muséum National d’Histoire
Naturelle, Paris, France; MNP, Museo Nacional de Panamá,
Panamá; MNRJ, Museu Nacional do Rio de Janeiro, Rio de
Janeiro, Brazil; MPBC, Museo de Paleontología Rodrigo
Botet (= Museu de Ciències Naturals de València), Valencia,
Spain; NRM, Swedish Museum of Natural History, Stock−
holm, Sweden; ROM, Royal Ontario Museum, Toronto, Ca−
BARGO ET AL.—HYPSODONTY IN PLEISTOCENE GROUND SLOTHS
55
50 mm
nada; UF, University of Florida, Vertebrate Paleontology
Collection, Gainesville, USA; USNM, National Museum of
Natural History, Smithsonian Institution, Washington, USA;
ZMUC, Zoologisk Museum Universitat Copenhagen, Co−
penhagen, Denmark.
Other abbreviations.—DM, depth of the mandible; HI, Hyp−
sodonty Index (HI = mandibular height/tooth row length ×
100); LTR, length of the molariform tooth row; OSA, occlusal
surface area.
Material and methods
The taxa analyzed included the mylodontids Glossotherium
robustum (Owen, 1842), Lestodon armatus Gervais, 1855,
Mylodon darwini Owen, 1839, and Scelidotherium lepto−
cephalum Owen, 1840 from southern South America; Para−
mylodon harlani (Owen, 1840) from North America; and the
megatheriids Megatherium americanum from southern
South America, M. altiplanicum, M. tarijense, M. medinae
from north central and northwestern South America, Eremo−
therium laurillardi from northern South America and North
America, and E. eomigrans from Florida, USA (Figs. 1, 2).
The specimens studied are listed in Table 1.
As the morphologies of the mandible and dentition differ
between the megatheriines and mylodontids analyzed in this
study, HI was standardized as follows: depth of the mandible
(DM), measured at the level of the third molariform tooth, di−
vided by length of the molariform tooth row (LTR). Although
the indices obtained cannot be compared with those of ungu−
Fig. 2. A, B. Paramylodon harlani (Owen, 1840), early Pleistocene, Hills−
borough, Florida, USA. A. Left upper caniniform, UF 87042. B. Left M2,
UF 87068. C, D. Glossotherium robustum (Owen, 1842), Pleistocene,
General Belgrano, Buenos Aires province, Argentina. C. Left upper
caniniform, MHM no catalogue number. D. Left M3, MHM no catalogue
number.
lates, they represent a useful reference for comparing the de−
gree of hypsodonty among ground sloths.
Results
Table 1 provides the list of studied specimens. Table 2 pro−
vides specimen measurements and calculated HI. Table 3
includes the means and standard deviations, where applica−
ble, for each species. In mylodontids mean HI ranges be−
tween 0.62 (Lestodon armatus) and 0.91 (Scelidotherium
leptocephalum). HI of Glossotherium robustum and Para−
Table 1. List of specimens.
Mylodontidae
Glossotherium robustum
MLP 3−136
MLP 3−138
MLP 3−140
Lestodon armatus
MLP 3−3
MLP 3−28
MLP 3−29
MLP 3−30
Mylodon darwini
MACN 991
MLP 3−125
MLP 3−126
Paramylodon harlani
LACMHC 1718−LR−20
LACMHC 1718−LR−21
LACMHC 1718−LR−24
LACMHC 1718−LR−25
LACMHC 1718−LR−26
LACMHC 1718− LR−27
LACMHC 1718−LR−28
LACMHC 1718−LR−29
LACMHC 1718−L6−R8
LACMHC 1718−L−16
LACMHC 1718−R−16
LACMHC 1718−L−9
LACMHC 1718−R−15
LACMHC 1718−L−36
LACMHC 1718−LR−30
LACMHC 22000
LACMHC 1718−LR−19
LACMHC 1717−32
Scelidotherium leptocephalum
MLP 3−401
MLP 3−420
MLP 3−456
MLP 3−671
MMP 157−S
MMP 549−S
MMP 1155−M
Megatheriidae
Megatherium americanum
MLP 2−37
MLP 2−50
MLP 2−52
MLP 2−54
MLP 2−56
MLP 2−58
MLP 2−59
MLP 2−60
MLP 2−207
MLP 27−VII−1−1
MLP 28−III−16−2
MLP 44−XII−28−1
MACN 1000
MACN 2831
MACN 2832
MACN 5002
MACN 15154
MNHNM 6
MNHNP R247
MPBC 1
BMNH 19953
BMNH 19953f
FMNH P14293
ZMUC 212
M. tarijense
FMNH P14216
NRM M4890
M. medinae
SGO PV236
SGO PV252
SGO PV288
SGO PV5000
M. altiplanicum
MNHN AYO 101
Eremotherium laurillardi
MCL 1700/02
MCL 1701/02
MCL 1702/02
MCL 7225
MCL 7229
MCL 7231
MCL 7233
MNRJ 2225
MNRJ 3858
MNP 44
MNP 46
USNM 18498
USNM 20867
ILSB s/n
AMNH 95742
F:AM s/n
ROM 40324
E. eomigrans
UF 121737
http://app.pan.pl/acta51/app51−053.pdf
56
ACTA PALAEONTOLOGICA POLONICA 51 (1), 2006
Table 2. Hypsodonty index of the ground sloths. LTR, length of the
tooth row; DM, depth of the mandible; HI, Hypsodonty Index.
Taxa
G. robustum
MLP 3−136
MLP 3−138
MLP 3−140
L. armatus
MLP 3−3
MLP 3−28
MLP 3−29
MLP 3−30
MMP 47−S
M. darwini
MACN 991
MLP 3−125
MLP 3−126
P. harlani
LACMHC1718−LR−21
LACMHC1718−LR−24
LACMHC1718−LR−25
LACMHC1718−LR−26
LACMHC1718−LR−27
LACMHC1718−LR−28
LACMHC1718−LR−29
LACMHC1718−L6−R8
LACMHC1718−L−16
LACMHC1718−L−9
LACMHC1718−R−15
LACMHC1718−L−36
LACMHC1718−LR−30
LACMHC22000
LACMHC1718−LR−19
LACMHC1717−32
LACMHC1718−LR−20
S. leptocephalum MLP s/n
MLP 3−420
MLP s/n
MLP 3−456
MMP 157−S
MMP 549−S
MMP 1155−M
M. americanum MLP 2−37
MLP 2−50
MLP 2−52
MLP 2−54
MLP 2−56
MLP 2−58
MLP 2−59
MLP 2−60
MLP 2−207
MLP 28−III−16−2
MLP 44−XII−28−1
MACN 1000
MACN 2831
MACN 2832
MACN 5002
MNHNM 6
MNHNP R247
MPBC 1
BMNH 19953
BMNH 19953f
FMNH P14293
ZMUC 212
LTR
130
128
130
190
175
170
160
165
126
137
131
136.3
142.9
142.4
137.4
141.2
142.3
140.0
130.6
142.2
134.6
139.0
123.7
150.0
145.6
136.0
144.0
127.7
101
113
108
107
101
98
116
239
192
220
192
200
201
206
186
202
213
223
212
237
231
228
209
211
215
259
201
216
193
DM
90
95
93
124
101
99
103
105
110
105
94
95.2
103.5
94.5
93.2
96.0
97.6
104.6
100.6
89.2
98.2
96.7
96.8
95.1
95.8
94.3
105.2
102.0
103
95
94
93
90
101
100
242
182
222
215
207
214
191
180
201
215
235
227
210
216
205
206
227
235
254
227
213
220
HI
0.69
0.74
0.71
0.65
0.58
0.58
0.64
0.63
0.87
0.76
0.71
0.69
0.72
0.66
0.68
0.68
0.68
0.75
0.77
0.63
0.73
0.7
0.78
0.63
0.66
0.69
0.73
0.8
1.01
0.84
0.87
0.87
0.89
1.03
0.86
1.01
0.95
1.00
1.12
1.04
1.06
0.93
0.97
1.00
1.01
1.05
1.07
0.89
0.94
0.90
0.99
1.08
1.09
0.98
1.13
0.99
1.14
M. tarijense
M. medinae
M. altiplanicum
E. laurillardi
E. eomigrans
FMNH P14216
NRM M4890
SGO PV236
SGO PV252
SGO PV288
SGO PV5000
MNHN AYO 101
MCL 1700/02
MCL 1701/02
MCL 1702/02
MCL 7225
MCL 7229
MCL 7231
MCL 7233
MNRJ 2225
MNRJ 3858
MNP 44
MNP 46
USNM 18498
USNM 20867
ILSB s/n
AMNH 95742
F:AM s/n
ROM 40324
UF 121737
152
204
172
151
142
130
143.6
196
186
174
190
182
188
194
198
192
193
186
185
185
196
182
200
193
215
140
169
161
142
116
118
145.0
152
136
127
146
141
143
152
153
142
152
143
143
136
152
151
151
156
169
0.92
0.82
0.93
0.94
0.81
0.90
1.01
0.77
0.73
0.73
0.77
0.77
0.76
0.78
0.77
0.74
0.79
0.77
0.77
0.73
0.78
0.83
0.76
0.81
0.78
mylodon harlani are equal (0.71), and that of Mylodon
darwini slightly higher (0.78). In megatheriines HI ranges
between 0.77 (Eremotherium laurillardi) and 1.02 (Mega−
therium americanum). HI in E. eomigrans (0.78) and M.
altiplanicum (1.01) are nearly identical to these extremes,
whereas it is intermediate in M. medinae and M. tarijense.
Discussion and conclusions
Hypsodonty, dietary behavior, habits, and habitat.—As
mentioned above, Janis (1988, 1995) and Janis and Fortelius
(1988) pointed out that habitat preference (closed or open)
would be as important as dietary preference in the develop−
ment of hypsodonty in ungulates. In other words, the abrasive
materials (dust and grit) accumulated on ground level plants or
dry environments should have influenced the evolution of
hypsodont teeth as much as the silica of the grasses. Recent
work (Williams and Kay 2001) has made it clear that both fac−
tors must figure strongly in discussions concerning the devel−
opment of hypsodonty in several “epitherian” groups.
The two groups under consideration (Megatheriidae and
Mylodontidae) are morphofunctionally distinct from each
other, but taxa within each group are markedly similar to
each other. De Iuliis (1996) noted that the masticatory appa−
ratus of Megatheriinae taxa (for which the skull is adequately
known) varies mainly in degree of hypsodonty and in fea−
tures related to hypsodonty. For example, the maxilla and
dentary are deeper in Megatherium americanum than in
Eremotherium laurillardi, in order to accommodate their
higher molariforms. Biomechanically, however, the appara−
BARGO ET AL.—HYPSODONTY IN PLEISTOCENE GROUND SLOTHS
Table 3. Mean values of Hypsodonty Index (HI). n, sample size; SD,
standard deviation.
Species
Glossotherium robustum
Lestodon armatus
Mylodon darwini
Paramylodon harlani
Scelidotherium leptocephalum
Megatherium americanum
Megatherium tarijense
Megatherium medinae
Eremotherium laurillardi
n
3
5
3
17
7
22
2
4
17
HI
mean
0.71
0.62
0.78
0.70
0.91
1.02
0.87
0.90
0.77
SD
0.03
0.03
0.08
0.05
0.08
0.07
0.07
0.06
0.03
tuses of these species are essentially identical, suggesting
similar food processing capabilities. Bargo (2001a) indicated
that M. americanum had a strong bite force relative to mylo−
dontids. Its masticatory movements were predominantly ver−
tical, with mediolateral movement restricted.
The analysis of occlusal surface area (OSA) by Vizcaíno
et al. (in press) indicates that Megatherium americanum has
an expected, or even higher, OSA value for a mammal of its
size, suggesting that M. americanum (and almost certainly
also E. laurillardi) was well suited for food processing in the
oral cavity, while the opposite is the case in mylodontids.
However, this feature is probably related to the digestive effi−
ciency of sloths rather than with the type of food taken
(Vizcaíno et al. in press). Further, the teeth of both mega−
theriines are bilophodont, forming a battery of high−crested
lophs. The sagittal section of each loph is triangular with a
sharp blade of hard dentine at the apex. This morphology in−
dicates that tough fibrous food, which requires grinding, did
not constitute the most appropriate dietary item. Instead, M.
americanum and E. laurillardi were apparently better suited
for consuming a variety of turgid or moderate to soft tough
food items. As this dental morphology precludes grazing,
this dietary mode was not an important factor influencing
hypsodonty in megatheriines.
Bargo and De Iuliis (1999) and De Iuliis et al. (2000)
noted that the distribution of the contemporaneous mega−
theriines Megatherium americanum and Eremotherium lau−
rillardi broadly coincided with temperate and tropical New
World regions, with M. americanum present mainly in south−
ern South America and E. laurillardi ranging from Brazil to
the southeastern United States. These authors suggested that
the difference in hypsodonty between these megatheriines
might be explained as adaptations to these different environ−
ments as reflected by their geographical distributions. E.
laurillardi inhabited more tropical to subtropical, closed or
forested environments, and is considerably less hypsodont
than M. americanum, which inhabited a more temperate, arid
to semiarid environment.
Relevant paleoecological information for the other Mega−
therium species is not available in the published literature.
57
Megatherium altiplanicum is from the Altiplano of Bolivia
and has an HI nearly equivalent to that of M. americanum. The
other two species considered here, M. medinae and M. tari−
jense, are known primarily from elevations approximately in−
termediate between those of M. americanum and M. alti−
planicum (see Saint−André and De Iuliis 2001), and their HI is
intermediate between that of M. americanum and M. alti−
planicum, on the one hand, and E. laurillardi, on the other.
While it is tempting to postulate that this altitudinal cline in HI
might be explained by environmental factors (i.e., the high el−
evation for M. altiplanicum being equivalent in terms of vege−
tation coarseness or grit as in the temperate lowland for M.
americanum), this hypothesis must remain speculative pend−
ing further investigations of the paleoecology of the areas
concerned.
Based on morphological and biomechanical analyses,
Bargo (2001b) demonstrated that the masticatory apparatus
of mylodontids was not particularly suited for producing
strong bite forces during mastication, and that the main
masticatory movement was anteromedial. This evidence
suggests that mylodonts were not well suited for extensive
oral food processing. Moreover, Vizcaíno et al. (in press)
found that mylodontids have extremely low OSA values in
comparison with living herbivorous mammals of equivalent
body size, which also suggests that mylodonts had poor food
oral processing. Bargo (2001b) also analyzed the relation−
ship between dietary habits and shape and width of the muz−
zle in sloths, which has been studied in ungulates by various
authors (Janis and Ehrhardt 1988 and references therein;
Solounias and Moelleken 1993). The results of Bargo’s
(2001b) analysis suggest that Lestodon and Glossotherium
were bulk feeders (i.e., mainly grazers) while Mylodon and
Scelidotherium were more selective, that is, browsers. These
dietary regimes do not correlate well with the pattern of HI
for mylodonts: Scelidotherium has the highest hypsodonty
index, followed by Mylodon, while Lestodon and Glosso−
therium have the lowest indices, which is the reverse of the
traditionally expected pattern of grazers having more hypso−
dont teeth than browsers. As noted above, however, the na−
ture of food items is not necessarily the most important or
only factor influencing hypsodonty, and factors other than
typical grazing habits must be considered in explaining the
pattern of hypsodonty in mylodontids. Recent ecomorpholo−
gical studies in living ungulates (Mendoza et al. 2002) have
indicated that a combination of (rather than any single) vari−
ables must be considered for prediction of dietary habits. One
obvious factor is an increased presence of grit caused by en−
vironmental differences resulting from geographic distribu−
tion (as noted above for megatheriines) or environmental
change over time, or particular habits (see below).
Evidence for distributional or temporal environmental
differences is lacking for South America, but the following
record of the North American mylodontid Paramylodon is
particularly relevant. Stock (1925) suggested that Paramylo−
don harlani was a grazer, a hypothesis followed by many
subsequent workers. But McDonald (1995) argued that the
http://app.pan.pl/acta51/app51−053.pdf
58
powerful forelimbs, with the expanded distal end of the hu−
merus, short radius, ulna with an enlarged olecranon process,
and dorsoventrally flattened unguals, permitted Paramylo−
don to dig up roots and tubers and he viewed Paramylodon as
an inhabitant of scrub or open country habitat. Independent
of the possible diets of Paramylodon harlani, McDonald
(1995) suggested that the greater hypsodonty observed in
Irvingtonian (early Pleistocene) individuals of this species as
compared to the more recent Rancholabrean (late Pleisto−
cene) individuals might reflect a change over time from
closed to more open habitats. This is an example of morpho−
logical change in a single species apparently in response to a
temporal, rather than geographic, environmental change.
Habit or behavior is also a factor to consider in hypso−
donty. Various authors (Owen 1842, 1856; Winge 1941;
Cuenca Anaya 1995; McDonald 1995) have postulated that
mylodontids obtained food by excavating the subterranean
portions of plant matter with their powerful forelimbs. The
biomechanical study by Bargo et al. (2000) supported the
hypothesis of digging behavior in mylodontids, which sug−
gests the ingestion of large quantities of abrasive soil ele−
ments. A study based on ichnological and geological evi−
dence in the Pampean region of South America (Vizcaíno
et al. 2001) demonstrated that Glossotherium robustum and
Scelidotherium leptocephalum were capable diggers and
excavated extensive burrows. This study not only indirectly
reinforces the hypothesis that these mylodontids might
have searched for food by digging, but further indicates that
abrasive soil particles were a major component of these
sloths’ environment, and thus that grit probably played a
role in the development of hypsodonty. The greater hypso−
donty in Scelidotherium may be an indirect indication that
digging behavior was more prevalent than in the other
mylodontids.
Mendoza et al. (2002) demonstrated that, at least in un−
gulates, adaptation to a given trophic niche involves com−
plex patterns of covariation between many morphological
characters of the skull and mandible. The lack of living ana−
logues to the ground sloths precludes performing appropri−
ate ecomorphological analyses to establish unequivocal cor−
relations between feeding behavior and morphological vari−
ables. Thus we cannot determine the degree to which higher
hypsodonty values in megatheriids and mylodontids corre−
spond to feeding on abrasive grasses rather than on browse,
as has been done for living ungulates (Janis 1988; Solounias
and Dawson−Saunders 1988), simply because we cannot
know the proportion of grass in their diet. However, the
available evidence allows us to state that habitat and burrow−
ing habit are evident factors in explaining differences in
hypsodonty in Pleistocene ground sloths. Differences in
habitat, such as between closed and open environments,
were apparently important in mylodontids, as well as in
megatheriines. In addition, morphologic and biomechanical
analyses in mylodontids indicate that digging behavior, in−
cluding but not limited to searching for food, played a con−
siderable role in shaping the dental characteristics of these
ACTA PALAEONTOLOGICA POLONICA 51 (1), 2006
sloths. In each case, the important agent was the relative
abundance of abrasive soil particles. Other morphological
variables may influence the degree of hypsodonty. Such
variables include OSA, crown features such as presence of
lobes or lophs, hardness of dentine, and perimeter length. It
is the interplay among these variables, often phylogeneti−
cally constrained, as well as abrasive particles in the food
and environment, that determine hypsodonty. Covariance
between skull and jaw variables has been proposed for other
xenarthrans. For instance, Vizcaíno et al. (in press) noted
that among pampatheres, a reduction in tooth lobation is
compensated by a considerable increase in OSA.
Phylogenetic constraint to hypsodonty.—Among Tardi−
grada, and indeed Xenarthra in general, hypsodonty is appar−
ently affected by diet, habitat and habit, but the individual
contributions of these factors cannot be as clearly partitioned
as in “epitherians” because the role of another factor, the ab−
sence of enamel, must be considered. Enamel is absent in the
teeth of all xenarthrans (when teeth, of course, are present),
except probably in the Eocene armadillo Utaetus (Simpson
1931). As discussed by Vizcaíno and De Iuliis (2003), this
absence of enamel has been a strong developmental con−
straint that has influenced the morphology of xenarthran
dentitions in such a way as to narrow the range of possible
morphological responses compared with those occurring in
“epitherians”. These authors demonstrated that xenarthrans
nonetheless possess morphological adaptations that allow
interpretations of their feeding behaviors, but that these
features are usually much more subtle than those evolved
among “epitherians” (see also Vizcaíno 1994a; Vizcaíno and
Fariña 1997; Vizcaíno and Bargo 1998; Vizcaíno et al. 1998;
De Iuliis et al. 2000; Fariña and Vizcaíno 2001; Bargo 2001a,
b, 2003; Vizcaíno et al. 2004, in press).
Certainly all xenarthrans (except the anteaters, the only
true “edentates”) have teeth that are relatively hypsodont
(i.e., they are tall with respect to their occlusal area), regard−
less of their particular dietary and feeding modes, in contrast
to “epitherians”. This is true despite the generally myrme−
cophagous to broadly omnivorous behaviors of armadillos,
the grazing behaviors of glyptodonts and pampatheres, and
the browsing, omnivorous and grazing behaviors of sloths.
“Epitherians” are much more variable in this regard; omni−
vory is never associated with hypsodonty, for example. In
this respect, variation in hypsodonty among “epitherians”
may be appropriately explained almost entirely in terms of
exclusively adaptational scenarios related to environmental
factors affecting wear.
It is, however, highly probable that the absence of ena−
mel, which would make the teeth less durable and wear down
faster, is responsible for much of the hypsodonty observed in
xenarthrans. In other words, the presence of high crowned
teeth is not an adaptational response to particular selection
pressures affecting wear, as seems likely in “epitherians”,
but a general requirement of xenarthrans. In this context the
term hypsodonty does not necessarily reflect convergent de−
BARGO ET AL.—HYPSODONTY IN PLEISTOCENE GROUND SLOTHS
velopments in xenarthrans and “epitherians”. The require−
ment of high crowned teeth results in similar indices among
different sloths, which tends to obscure the possible reasons
for the comparatively small differences in relative tooth
height. While the presence of hypsodonty itself cannot be ex−
plained mainly by the reasons typically given for “epithe−
rians” (e.g., grazing versus browsing; open versus closed
habitats), differences in hypsodonty among sloths apparently
do correlate with dietary behavior, habits and habitat, sug−
gesting that they are appropriate for explaining the variation
in sloths as well.
Further considerations on the evolution of hypsodonty in
South America.—Increased tooth height in xenarthrans ap−
pears to be part of a common adaptive strategy among South
American mammal lineages. Clearly, hypsodonty was ac−
quired independently in xenathrans and “epitherians” but
hypsodonty also seems to have occurred among multiple, di−
verse South American mammalian taxa. For example, South
American gondwanatherians acquired hypsodonty earlier
than and independently of therians. The trait had arisen by
the Late Cretaceous (Koenigswald et al. 1999) and persisted
until the Paleocene. In xenarthrans hypsodonty had already
arisen by the late Paleocene, based on the first record of the
group. The earliest teeth of this group are known from arma−
dillos whose mandibles and teeth are very similar to those of
the living Dasypus novemcinctus (Vizcaíno 1994b), a spe−
cies that is clearly not a “grazer,” but essentially animali−
vorous (Redford 1985; Vizcaíno et al. 2004). By the Paleo−
cene hypsodonty had not clearly developed in the already di−
verse South American ungulates (Notoungulata, Litopterna,
Astrapotheria, Pyrotheria). Bond (1986) stated that brachy−
dont cheek teeth were characteristic of most ungulate lin−
eages, with only some groups of notoungulates showing a
tendency to increase tooth crown height, a tendency accentu−
ated by the early Eocene. Later changes in degree of hypso−
donty among essentially plant feeding xenarthrans such as
glyptodonts and sloths apparently reflect adaptation to differ−
ent diets, feeding behaviors, or environmental conditions.
Pascual and Ortiz Jaureguizar (1990) stated that, during the
latest part of the Cenozoic, many xenarthrans (in addition to
ungulates), as well as varied gigantic native rodents, fol−
lowed a similar dental modification pattern, from a low−
crowned to high−crowned morphology, in response to gen−
eral environmental and climatic trends from predominantly
closed−forested, warm and wet habitats to open temperate
grasslands, to hot deserts, or to cold habitats. These authors
further noted that this general pattern was also detectable in
smaller native rodents (Kraglievich 1940), and some peculiar
marsupials convergent on the rodent adaptive zone (Pascual
et al. 1988), and primates (Kay et al. 2002). The evolution of
hypsodonty in diverse mammalian lineages during the Ceno−
zoic is also recorded in other continents; i.e., North America
(Stirton 1947; Janis 1988, 1995), Africa (Bobe et al. 2004),
Europe (Jernvall and Fortelius 2002) and Eurasia (Fortelius
et al. 2002). However, differences in the quality of databases
59
hinder comparison of this process among different conti−
nents. For instance, while hypsodonty degree is recorded in
extensive databases of Neogene fossil mammals from Eur−
asia (NOW: http://www.helsinki.fi/science/now/) and Africa
(see Bobe et al. 2004, ETE Program), a comparable tool is as
yet unavailable for South America.
The repeated occurrence of hypsodonty in so many diverse
and even unrelated lineages leads one to wonder whether there
is some peculiarity of the South American continent that has
led so many lineages along the path to hypsodonty. Although
this may appear far fetched, similar thoughts have been ex−
pressed with respect to folivory (van Schaik et al. 1993). Un−
fortunately, current knowledge of the paleobiology and eco−
morphology of South American mammals is far too incom−
plete to provide a definitive answer; and much work remains
to be done on the various lineages, especially those with a
long history in the continent (in this respect, the Xenarthra
has clearly received the most attention in the past decade).
We suggest that one possible factor is the long geographic
isolation of the continent. This imposed ecological relation−
ships that are not readily understood using the parameters
that apply to the Old World (and the connected North Amer−
ica) and require different explanatory models (e.g., Fariña
1996; Croft 2001).
Acknowledgements
We are grateful to Richard Kay (Duke University, Durham, USA) and
two anonymous reviewers for their valuable comments and suggestions
that improved the manuscript. This paper is a contribution to the follow−
ing projects: Universidad Nacional de La Plata N336 and PIP−CONICET
5240.
References
Bargo, M.S. 2001a. The ground sloth Megatherium americanum: skull
shape, bite forces, and diet. Acta Paleontologica Polonica 46: 173–192.
Bargo, M.S. 2001b. El aparato masticatorio de los perezosos terrestres
(Xenarthra, Tardigrada) del Pleistoceno de la Argentina. Morfometría y
biomecánica. 400 pp. Unpublished Ph.D. thesis. Universidad Nacional de
La Plata, La Plata.
Bargo, M.S. and De Iuliis, G. 1999. Hypsodonty and bilophodonty in
Megatherium americanum (Xenarthra, Tardigrada): a paradox. In: B.
Shockey and F. Anaya (eds.), Abstracts of the Congress Neotropical
Evolution of the Cenozoic, 11. La Paz.
Bargo, M.S., Vizcaíno, S.F., Archuby, F.M., and Blanco R.E. 2000. Limb
bone proportions, strength and digging in some Lujanian (late Pleisto−
cene–early Holocene) mylodontid ground sloths (Mammalia, Xenarthra).
Journal of Vertebrate Paleontology 20: 601–610.
Bobe Quinteros, R., Behrensmeyer, A.K., and Carrasco−Ormazábal, A.G.
2004. Paleoclima y evolución faunística en el Plio−Pleistoceno de
África y América del Sur. Ameghiniana 41: 641–649.
Bond, M. 1986. Los ungulados fósiles de Argentina: evolución y paleo−
ambientes. IV Congreso Argentino de Paleontología y Bioestratigrafía
Actas 2: 173–185.
Cuenca Anaya, J. 1995. El aparato locomotor de los escelidoterios (Eden−
tata, Mammalia) y su paleobiología. 452 pp. Colección “Estudis” 6,
Adjuntament de València, València.
http://app.pan.pl/acta51/app51−053.pdf
60
Croft, D.A. 2001. Cenozoic environmental change in South America as in−
dicated by mammalian body size distributions (cenograms). Diversity
and Distributions 7: 271–287.
Cuvier, G. 1796. Notice sur le esquelette d’une très grande espèce de
quadrupède inconnue jusqu’à présent, trouvé au Paraguay, et déposé au
cabinet d’histoire naturelle de Madrid. Magasin encyclopèdique, ou
Journal des Sciences, des Lettres et des Arts 1: 303–310; 2: 227–228.
De Iuliis, G. 1996. A systematic review of the Megatheriinae (Mammalia:
Xenarthra: Megatheriidae). 719 pp. Unpublished Ph.D. thesis, Univer−
sity of Toronto, Toronto.
De Iuliis, G. and Cartelle, C. 1999. A new giant megatheriine ground sloth
(Mammalia: Xenarthra: Megatheriidae) from the late Blancan to early
Irvingtonian of Florida. Zoological Journal of the Linnean Society 127:
495–515.
De Iuliis, G., Bargo, M.S., and Vizcaíno, S.F. 2000. Skull morphology varia−
tion and mastication in the fossil giant armadillos Pampatherium spp.;
with remarks on related genera (Mammalia: Xenarthra: Pampatheriidae).
Journal of Vertebrate Paleontology 20: 743–754.
Delsuc, F., Vizcaíno, S.F., and Douzery, E. 2004. Influence of Tertiary
paleoenvironmental changes on the diversification of South American
mammals: a relaxed molecular clock study within xenarthrans. BMC
Evolutionary Biology 4: 1–13.
Fariña, R.A. 1996. Trophic relationships among Lujanian mammals. Evolu−
tionary Theory 11: 125–134.
Fariña, R.A., and Vizcaíno, S.F. 2001. Carved teeth and strange jaws: How
glyptodonts masticated. Acta Paleontologica Polonica 46: 87–102.
Fortelius, M. 1985. Ungulate cheek teeth: developmental, functional, and
evolutionary interrelations. Acta Zoologica Fennica 180: 1–76.
Fortelius, M., Eronen, J., Jernvall, J. Liu, L., Pushkina, D., Rinne, J., Tesa−
kov, A., Vislobokoba, I., Zhang, Z., and Zhou, L. 2002. Fossil mammals
resolve regional patterns of Eurasian climate change over 20 million
years. Evolutionary Ecology Research 4: 1005–1016.
Gervais, P. 1855. Recherches sur les mammifères fossils de l´Amérique
méridionale. Annales des Sciences Naturelles, Zoologie 3: 330–338.
Gervais, H. and Ameghino, F. 1880. Los mamíferos fósiles de la América del
Sud. 225 pp. F. Sabih−Igon, Paris.
Hoffstetter, R. 1958. Xenarthra. In: J. Piveteau (ed.), Traité de paléontologie,
Vol. 6, 535–636. Masson, Paris.
Janis, C.M. 1988. An estimation of tooth volume and hypsodonty indices in
ungulate mammals, and the correlation of these factors with dietary prefer−
ence. In: D.E. Russell, J.P. Santoro, and D. Sigogneau−Russell (eds.),
Teeth revisited: Proceedings of the VII International Symposium on Den−
tal Morphology. Memoirs du Muséum national d’Histoire naturelle (série
C) 53: 367–387.
Janis, C.M. 1995. Correlations between craniodental morphology and feed−
ing behavior in ungulates: reciprocal illumination between living and
fossil taxa. In: J. Thomason (ed.), Functional Morphology in Vertebrate
Palaeontology, 76–98, Cambridge University Press, New York.
Janis, C.M. and Ehrhardt, D. 1988. Correlation of the muzzle width and rela−
tive incisor width with dietary preference in ungulates. Zoological Jour−
nal of the Linnean Society 92: 267–284.
Janis, C.M. and Fortelius, M. 1988. On the means whereby mammals
achieve increased functional durability of their dentitions, with special
reference to limiting factors. Biological Review 63: 197–230.
Jernvall, J. and Fortelius, M. 2002. Common mammals drive the evolution−
ary increase of hypsodonty in the Neogene. Nature 417: 538–540.
Kay, R.F., Williams, B.A., and Anaya, F. 2002. The adaptations of Branisella
boliviana, the earliest South American monkey. In: J.M. Plavcan, R.F.
Kay, W.L. Jungers, and C.P. van Schaik (eds.), Reconstructing Behavior
in the Primate Fossil Record, 339–370. Kluwer Academic/Plenum Publi−
cations, New York.
Koenigswald, W. von, Goin, F. and Pascual, R. 1999. Hypsodonty and
enamel microstructure in the Paleocene gondwanatherian mammal
Sudamerica ameghinoi. Acta Palaeontologica Polonica 44: 263–300.
Kraglievich, L. 1930. La formación friaseana del Río Frías, Río Fénix,
Laguna Blanca, etc. y su fauna de mamíferos. Physis 10: 127–161.
Kraglievich, J.L. 1940. Morfología normal y morfogénesis de los molares
ACTA PALAEONTOLOGICA POLONICA 51 (1), 2006
de los carpinchos y caracteres filogenéticos de este grupo de roedores.
Obras completas y trabajos científicos inéditos 3: 339–494.
Lund, P.W. 1842. Blik paa Brasiliens Dyreverden for Sidste Jordomvaeltning.
Fjerde Afhandling: Fortsaettelse af Pattedyrene. Detkongelige Danske
Videnskabernes Selskabs Skrifter Naturvidenskabelige og Mathematisk
Afhandlinger 9: 137–208.
MacFadden, B.J. 1997. Origin and evolution of the grazing guild in New
World terrestrial mammals. Trends in Ecology and Evolution 12:
182–187.
Madsen, O., Scalli, M., Douady, C.J., Kao, D.J., DeBry, R.W., Adkins, R.,
Amrine, H.M., Stanhope, M.J., de Jong, W.W., and Springer, M.S.
2001. Parallel adaptative radiations in two major clades of placental
mammals. Nature 409: 610–614.
McDonald, H.G. 1995. Gravigrade xenarthrans from the Early Pleistocene
Leisey Shell Pit 1A, Hillsborough County, Florida. Bulletin of the
Florida Museum of Natural History 37: 345–373.
McDonald, H.G. 1997. Xenarthrans: Pilosans. In: R.F. Kay, R.H. Madden,
R.L. Cifelli, and J.J. Flynn (eds.), Vertebrate Paleontology in the
Neotropics. The Miocene fauna of La Venta, Colombia, 233–245.
Smithsonian Institution Press, Washington D.C.
McKenna, M.C. 1975. Toward a phylogenetic classification of the Mammalia.
In: W.P. Luckett and F.S. Szalay (eds.), Phylogeny of the Primates, 21–46,
Plenum Publishing Corporation, New York.
McNaughton, S.J., Tarrants, J.L., McNaughton, M.M., and Davis, R.H.
1985. Silica as a defense against herbivory and a growth promotor in Af−
rican grasses. Ecology 66: 528–535.
Mendoza, M., Janis, C., and Palmqvist, P. 2002. Characterizing complex
craniodental patterns related to feeding behavior in ungulates: a multi−
variate approach. Journal of Zoology London 258: 223–246.
Murphy, W.J, Eizirik, E, Johnson, W.E., Zhang, Y.P., Ryderk, O.A., and
O’Brien, S.J. 2001. Molecular phylogenetics and the origins of placen−
tal mammals. Nature 409: 614–618.
Owen, R. 1839. Fossil Mammalia (2). In: C.R. Darwin (ed.), The Zoology of
the Voyage of the Beagle, 1 (7), 41–64. Smith, Elder and Co., London.
Owen, R. 1840. Fossil Mammalia (4). In: C.R. Darwin (ed.), The Zoology of
the Voyage of the Beagle, 1 (13), 81–111. Smith, Elder and Co., London.
Owen, R. 1842. Description of the Skeleton of an Extinct Gigantic Sloth,
Mylodon robustus, Owen, with Observations on the Osteology, Natural
Affinities, and Probable Habits of the Megatherioid Quadruped in Gen−
eral. 176 pp. R. and J.E. Taylor, London.
Owen R. 1856. On the Megatherium (Megatherium americanum Cuvier and
Blumenbach). III. The skull. Philosophical Transactions of the Royal
Society of London 146: 571–589.
Pascual, R., Carlini, A.A., and De Santis, L.J. 1988. Dentition and ways of life
in Cenozoic South American rodent−like marsupials. Outstanding exam−
ples of convergence. In: D.E. Russell, J.P. Santoro, and D. Sigogneau−
Russell (eds.), Teeth Revisited: Proceedings of the VII International Sym−
posium on Dental Morphology. Mémoires du Muséum national d’Histoire
naturelle (Série C) 53: 217–226.
Pascual, R. and Ortiz Jaureguizar E. 1990. Evolving climates and mammal
faunas in Cenozoic South America. Journal of Human Evolution 19:
23–60.
Philippi, R.A. 1893. Vorläufige Nachricht über fossile Säugethierknochen
von Ulloma, Bolivia. Zeitschrift der deutschen geologischen Gesell−
schaft 45: 87–96.
Redford, K.H. 1985. Food habits of Armadillos (Xenarthra: Dasypodidae). In:
G.G. Montgomery (ed.), The Evolution and Ecology of Armadillos, Sloths
and Vermilinguas, 429–437. Smithsonian Institution Press, Washington
D.C.
Saint−André, P.A. and De Iuliis, G. 2001. The smallest and most ancient repre−
sentative of the genus Megatherium Cuvier, 1796 (Xenarthra, Tardigrada,
Megatheriidae), from the Pliocene of the Bolivian Altiplano. Geodi−
versitas 23: 625–645.
Scillato−Yané, G.J. 1986. Los Xenarthra fósiles de Argentina (Mammalia,
Edentata). IV Congreso Argentino de Paleontología y Bioestratigrafía
2: 151–165.
Scillato−Yané, G.J., Carlini, A.A., and Vizcaíno, S.F. 1987. Nuevo Nothro−
BARGO ET AL.—HYPSODONTY IN PLEISTOCENE GROUND SLOTHS
theriinae (Edentata, Tardigrada) de Edad Chasiquense (Mioceno tardío)
del sur de la Provincia de Buenos Aires (Argentina). Ameghiniana 24:
211–215.
Simpson, G.G. 1931. A new classification of mammals. Bulletin of the
American Museum of Natural History 59: 259–293.
Simpson, G.G. 1951. Horses: The Story of the Horse Family in the Modern
World and Through Sixty Million Years of History. 247 pp. Oxford Uni−
versity Press, New York.
Simpson, G.G. 1953. The Major Features of Evolution. 434 pp. Columbia
University Press, New York.
Solounias, N. and Dawson−Saunders, B. 1988. Dietary adaptations and
palaeoecology of the late Miocene ruminants from Pikermi and Samos
in Greece. Palaeogeography, Palaeoclimatology, Palaeoecology 65:
149–172.
Solounias, N. and Moelleken, S.M. 1993. Dietary adaptation of some extinct
ruminants determined by premaxillary shape. Journal of Mammalogy
74: 1059–1071.
Stirton, R.A. 1947. Observations on evolutionary rates in hypsodonty. Evo−
lution 1: 32–41.
Stock C. 1925. Cenozoic Gravigrade Edentates of Western North America,
with Special Reference to the Pleistocene Megalonychidae and Mylo−
dontidae of Rancho La Brea. 206 pp. Carnegie Institution of Washing−
ton, Washington.
van Schaik, C.P., Terborgh, J.W., and Wright, S.J. 1993. The phenology of
tropical forests: adaptive significance and consequences for primary
consumers. Annual Review of Ecology and Systematics 24: 353–377.
Vizcaíno, S.F. 1994a. Mecánica masticatoria de Stegotherium tessellatum
Ameghino (Mammalia, Xenarthra) del Mioceno temprano de Santa Cruz
(Argentina). Algunos aspectos paleoecológicos relacionados. Ameghi−
niana 31: 283–290.
Vizcaíno, S.F. 1994b. Sistemática y Anatomía de los Astegotheriini Ameg−
hino, 1906 (nuevo rango) (Dasypodidae, Dasypodinae). Ameghiniana
31: 3–13.
Vizcaíno, S.F. and Bargo, M.S. 1998. The masticatory apparatus of Eutatus
61
(Mammalia, Cingulata) and some allied genera. Evolution and paleo−
biology. Paleobiology 24: 371–383.
Vizcaíno, S.F. and De Iuliis, G. 2003 Evidence for advanced carnivory in
fossil armadillos (Mammalia: Xenarthra: Dasypodidae). Paleobiology
29: 123–138.
Vizcaíno, S.F. and Fariña, R.A. 1997. Diet and locomotion of the armadillo
Peltephilus: a new view. Lethaia 30: 79–86.
Vizcaíno, S.F., Bargo. M.S., and Cassini, G.H. (in press). Dental occlusal
surface area in relation to body mass, food habits and other biologic fea−
tures in fossil xenarthrans. Ameghiniana 43 (1).
Vizcaíno, S.F., De Iuliis, G., and Bargo, M.S. 1998. Skull shape, masticatory
apparatus, and diet of Vassallia and Holmesina (Mammalia: Xenarthra:
Pampatheriidae). When anatomy constrains destiny. Journal of Mamma−
lian Evolution 5: 291–322.
Vizcaíno, S.F., Zárate, M., Bargo, M.S., and Dondas, A. 2001. Pleistocene
large burrows in the Mar del Plata area (Buenos Aires Province, Argen−
tina) and their probable builders. Acta Paleontologica Polonica 46:
157–169.
Vizcaíno, S.F., Fariña, R.A., Bargo, M.S., and De Iuliis, G. 2004. Phylo−
genetical assessment of the masticatory adaptations in Cingulata (Mam−
malia, Xenarthra). Ameghiniana 41: 651–664.
White, J.L. 1997. Locomotor adaptations in Miocene xenarthrans. In: R.F.
Kay, R.H. Madden, R.L. Cifelli, and J.J. Flynn (eds.), Vertebrate Pale−
ontology in the Neotropics. The Miocene Fauna of La Venta, Colombia,
246–264. Smithsonian Institution Press, Washington D.C.
Williams, S.H. and Kay, R.F. 2001. A comparative test of adaptive explana−
tions for hypsodonty in ungulates and rodents. Journal of Mammalian
Evolution 8: 207–229.
Winge, H. 1941. Edentates (Edentata). In: S. Jensen, R. Spärck, and H. Volsoe
(eds.), The Interrelationships of the Mammalia Genera, 319–341. Reitzels
Forlag, Copenhagen.
Zetti, J. 1964. El hallazgo de un Megatheriidae en el “Médano invasor” del
SW de Toay, Provincia de La Pampa. Ameghiniana 3: 257–265.
http://app.pan.pl/acta51/app51−053.pdf